Unlike a typical four-wheel vehicle, a motorcycle rider is not restrained to the vehicle body by a seat belt or the like. Therefore, to effectively restrain the rider, it is known, for example, to provide support belts that are fixed at one end to the vehicle body and at the other end to the air bag so that, upon inflation of the air bag, the air bag is supported by the connected support belts in addition to a case portion in which the air bag has been stored.
For example, Japanese Patent Laid-open No. 2003-327182 discloses an air bag system, for a motor scooter type motorcycle, in which support belts for an air bag are stored in a left-right pair of storing grooves provided over the range from a front cover through a leg shield and a foot mount portion to a rear cover. Accordingly, the rider can be restrained if the vehicle body displays large yawing and rolling behaviors, without having to enlarge the capacity of the air bag.